Vehicular hands-free telephone system

Abstract

A voice of user is picked up by a microphone built in a sun visor of a vehicle. The output of microphone is frequency-modulated by an FM transmitter powered by a solar battery and transmitted through a transmitting antenna in a vehicle. The frequency-modulated radio signal is received and demodulated by a receiver with a receiving antenna. The received signal is further transmitted outside of the vehicle through a transceiver.

What is claimed is: 
     
       1. A vehicular hands-free telephone apparatus comprising a microphone for converting an acoustic signal to an electrical signal,   an FM transmitter for generating a frequency-modulated radio signal in response to the output of said microphone,   a transmitting antenna for transmitting in a vehicle said radio signal generated from said FM transmitter,   a solar battery for converting light energy to electrical energy and providing operation power to said FM transmitter, said solar battery being mounted on a windshield of said vehicle,   a receiving antenna for receiving said radio signal transmitted from said transmitting antenna,   a receiver for receiving and frequency-demodulating said radio signal received by said receiving antenna, and   a transceiver for transmitting the output of receiver outside of said vehicle,   wherein said microphone, transmitting antenna and FM transmitter are built in a sun visor of said vehicle.   
     
     
       2. A vehicular hands-free telephone apparatus according to claim 1, wherein said operating power is provided from said solar battery to said FM transmitter through said transmitting antenna. 
     
     
       3. A vehicular hands-free telephone apparatus according to claim 1, wherein said receiving antenna is a leakage-type paired transmission cable.   
     
     
       4. A vehicular hands-free telephone apparatus according to claim 1, wherein said microphone has both forward and rear directionality.   
     
     
       5. A vehicular hands-free telephone apparatus according to claim 1, wherein said microphone is an electret capacitor microphone.   
     
     
       6. A vehicular hands-free telephone apparatus according to claim 1, wherein said FM transmitter includes a voice-activated switch circuit for enabling said FM transmitter only when a voice signal is detected.   
     
     
       7. A vehicular hands-free telephone apparatus according to claim 1, wherein said transmitting antenna is terminated at its end by a terminating resistor matched to the impedance of said paired transmission cable.   
     
     
       8. A vehicular hands-free telephone apparatus according to claim 1, wherein said apparatus further comprises a secondary battery which is charged by said solar battery.   
     
     
       9. A vehicular hands-free telephone apparatus according to claim 1, wherein a said secondary battery is connected so as to be charged by said solar battery through at least one reactance.   
     
     
       10. A vehicular hands-free telephone apparatus according to claim 1, wherein said secondary battery is charged by said solar battery through a diode for blocking a reverse current.   
     
     
       11. A vehicular hands-free telephone apparatus according to claim 1, wherein said transmitting antenna includes a DC blocking capacitor having a sufficiently small impedance value at the frequency of the transmitted radio signal.   
     
     
       12. A vehicular hands-free telephone apparatus according to claim 1, wherein said microphone is built in a sun visor of said vehicle and at least part of said sun visor disposed in front of said microphone is made of a permeable material that does not obstruct acoustic input.   
     
     
       13. A vehicular hands-free telephone apparatus according to claim 1, wherein said receiving antenna is a loop antenna mounted inside a phone base which includes said receiver.   
     
     
       14. A vehicular hands-free telephone apparatus according to claim 1, wherein said FM transmitter includes a circuit for rejecting higher harmonics in said frequency-modulated radio signal.